Viscous coupling apparatus with opposing coined plates

ABSTRACT

A viscous coupling apparatus having enhanced torque progression characteristics. The viscous coupling apparatus includes two sets of viscous coupling plates which are interleaved and mounted with rotatable members for relative rotation therebetween. Each plate is a generally circular ring of thin plate material and has one or more openings formed therein. The openings include coined edge surfaces that form an inclined surface and an arcuate wiping surface. The coined edges of inner and outer coupling plates oppose one another and facilitate the removal of viscouse fluid from in between and wiping of viscous fluid from the surface of adjacent coupling plates when relative rotation and frictional contact occurs between adjacent plates without generating excessive wear on either one of the plates. The removal of the viscous fluid promotes enhanced frictional contact between the facing adjacent plate surfaces and results in an increased torque transmission characteristic.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/059,636, filed on May 10, 1993, now U.S. Pat. No. 5,346,044,issued Sep. 13, 1994, which is a continuation-in-part of U.S. patentapplication Ser. No. 07/891,417, filed May 29, 1992, now U.S. Pat. No.5,232,075, issued Aug. 3, 1993, which is a continuation of U.S. patentapplication Ser. No. 07/720,401, filed Jun. 25, 1991, now U.S. Pat. No.5,148,900, issued Sep. 22, 1992.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates generally to a viscous coupling apparatusof the type used in motor vehicles and, more particularly, to animprovement in the viscous coupling plates utilized within the viscouscoupling apparatus.

Viscous couplings are used in various applications within the drivetrainof a motor vehicle. In one typical application, a viscous coupling islocated within the transfer case of a four-wheel drive vehicle to avoidtight corner braking by allowing slip to occur between the front andrear axles while concomitantly delivering torque to the wheel withtraction. In another vehicular application, the viscous coupling is usedin association with a differential to secure effective power deliveryand improve traction, handling and stability. In still anotherapplication, the viscous coupling is a viscous transmission device thatis located between the front and rear axles to provide "on-demand"four-wheel drive operation.

In general, viscous couplings include of a rotatable input member and arotatable output member, both members being rotatable about a commonaxis. The output member is often in the form of a hub while the inputmember is a rotatable housing that is hermetically sealed around the hubso as to define a chamber therebetween. Alternately, the input andoutput arrangements could be reversed in other applications. Within thechamber are two sets of viscous coupling plates. The first set ofplates, the inner viscous coupling plates, are splined to the hub androtate therewith. Similarly, a second set of plates, the outer viscouscoupling plates, are splined to the housing and rotate therewith. Theouter plates are interleaved with the inner plates. Filling the chamberor space between the housing and the hub is a high viscosity fluid, suchas silicone oil, and, usually, a small amount of gas or air.

In operation, if a slight difference in rotational speed occurs betweenthe input and output members, the relatively low shear rate occurringwithin the viscous fluid will permit relative slip to occur between therotating members. However, as the speed differential increases, theviscous shear rate also increases and the fluid works to transmit torquefrom the input hub to the output housing. As so far described, suchviscous couplings are well known in the motor vehicle field.

During initial operation of the viscous coupling, torque is primarilytransmitted by the shearing forces resulting from relative rotation ofthe adjacent viscous coupling plates. However, if continuous relativerotation between the input and output members occurs over a period oftime, a torque transmission phenomenon appears. This phenomenon is oftenreferred to as torque progression or "humping". During such a torqueprogression, the amount of torque transmitted between the input andoutput members substantially increases without a corresponding increasein relative rotation. More particularly, if the rotational speeddifferential continues to exist, shearing of the viscous fluid willproduce a temperature increase within the chamber. Concomitantly, theviscosity of the fluid decreases which, in turn, causes a predictabledigression in the amount of torque being transmitted. However, as thefluid temperature continues to rise, the pressure within the sealedchamber increases for causing a number of the coupling plates to axiallyshift relative to the input and output members. As the pressurecontinues to increase, adjacent inner and outer plates are forced intomating or frictional contact with one another which results in torquebeing transferred by a frictional component in addition to the alreadypresent viscous shear component. Once frictional contact has beenestablished between the plates, torque transmission is suddenly andsignificantly amplified producing the "humping" phenomenon stated above.

Because torque progression is partially caused by the surface to surfacefrictional contact of adjacent viscous coupling plates, the "humping"phenomenon can be enhanced if the space in between adjacent plates aswell as the plates' contacting surfaces can be made reasonably free ofthe viscous fluid. To this end, it would be advantageous to remove or"pump" the viscous fluid from in between adjacent plates and, inaddition, wipe their contacting surfaces substantially free from thefluid.

Viscous coupling plates are generally manufactured via a stampingoperation in a machine press from a thin sheet of plate material orstock. The press utilizes male and female dies which cause the couplingplates to conform to the desired configuration. Invariably, a stampedviscous coupling plate exhibits die roll (i.e. a rounded edge) on theedges of one side of the openings formed in the plate and a fine unevenburr on the edges of the opposing side. In operation, the uneven burr isquickly worn from the plate surface by the frictional forces whichproduce the amplified torque progression. Unfortunately, once the unevenburr has been worn from the plate surface, the viscous fluid introducedin between and onto the plate surfaces by the die roll cannot beeffectively removed.

Conventionally, die roll has been eliminated on some viscous couplingplates by milling the openings or slots formed therein so as to grindoff the die roll. Die roll has also been avoided by replacing thestamping process with laser cutting of the plates themselves. However,both of the above methods have not proven themselves to be costeffective and, in actuality, have proven to be difficult to duplicateand incorporate into a production setting. Another known method forproviding a wiping edge is to bend the edge of the viscous clutch plateas disclosed in U.S. Pat. No. 4,989,687. However, such bent edges mayproduce an overly aggressive (i.e. sharp) wiping edge that causesexcessive metal wear on the mating plates.

With the above discussion in mind, it is an object of the presentinvention to overcome the disadvantages associated with conventionalviscous coupling plates while enhancing the torque progressioncharacteristics of the viscous coupling apparatus.

It is another object of this invention to manufacture a viscous couplingplate which is configured to substantially remove viscous fluid from inbetween and wipe viscous fluid off the surfaces of adjacent couplingplates to thereby enhance the frictional contact of adjacent couplingplates without causing the increased wear on the plates.

A further object of the present invention is to produce a viscouscoupling plate having a raised surface which causes the removal ofviscous fluid from in between adjacent coupling plates and alsosubstantially wipes off fluid from the planar surface of an adjacentcoupling plate and which is not readily susceptible to frictionalwearing.

Another object of the invention is to incorporate the viscous couplingplates having enhanced frictional contact characteristics in a viscouscoupling apparatus so as to increase the torque capacity of the viscouscoupling apparatus.

Finally, it is also an object of this invention to produce a viscouscoupling plate for use in a viscous coupling apparatus which exhibitsthe above advantages and objects and which is cost effective to produce.

In achieving the above objects, the present invention provides for aviscous coupling apparatus which exhibits enhanced torque progressioncharacteristics and torque capacity and which can be cost effectivelyproduced. The viscous coupling plates of the present invention includeraised surfaces which are formed by coining the edges of the slotsand/or openings formed in the plates. The coined edges provide a wipingsurface that is offset from the general plane of the plate. The wipingsurface exhibits increased frictional wearability over that exhibited byconventional plates having an uneven burr. Also, fabrication of thecoupling plate may be accomplished in a cost effective manner in, forexample, a progressive die machine press. A first stamping operationforms the coupling plate in its general configuration. A second coiningoperation is then readily performed thereafter without removal of theplate from the machine press. The coupling plates of the presentinvention are positioned in the viscous coupling apparatus so that theraised surfaces of adjacent plates (i.e. inner and outer plates) opposeor face one another. In this configuration, the total contact force isdistributed between both the wiping surfaces of the inner plates and thewiping surfaces of the outer plates, thus increasing the overall contactsurface area than that exhibited in conventional viscous couplingapparatus. Correspondingly, wear in each individual coupling plate isreduced to thereby increase the useful life of the coupling plates.Also, because both opposing plates assist in the pumping action, thetotal contact force achievable between adjacent plates is significantlyincreased which, in turn, allows the torque capacity for each pair ofcoupling plates to likewise be increased.

Additional benefits and advantages of the present invention will becomeapparent to those skilled in the art to which this invention relatesfrom the subsequent description of a preferred embodiment and theappended claims, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an exemplary viscous coupling apparatushaving the viscous coupling plates according to the principles of thepresent invention;

FIG. 2 is a plan view of an inner viscous coupling plate utilized in theviscous coupling apparatus of FIG. 1;

FIG. 3 is a sectional view taken substantially along line 3--3 in FIG. 2illustrating the raised surfaces formed on the viscous coupling plateafter the stamping and coining operations;

FIG. 4 is a partial sectional view showing the burr and die rollassociated with a conventional stamped viscous coupling plate;

FIG. 5 is a partial sectional view showing a conventional stampedviscous coupling plate having milled edges for eliminating die roll;

FIG. 6 is a partial sectional view showing a conventional stampedviscous coupling plate formed with bent edges for defining a sharpwiping edge;

FIG. 7 is a detail view showing an enlarged section of the inner viscouscoupling plate depicted in FIG. 3;

FIG. 8 is a detail view showing an enlarged section of an outer viscouscoupling plate; and

FIG. 9 is a partial sectional view along line 9--9 of FIG. 1 showing theorientation of the inner and outer viscous coupling plates.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, a viscous coupling apparatus isillustrated in FIG. 1 and is generally designated at 10. Viscouscoupling apparatus 10 is merely exemplary of the type of device that canbe utilized in conjunction with a four-wheel drive transfer case orother aspects of a vehicle's drivetrain, including the front and reardifferentials, or as a viscous transmission for driving the rear orfront axle.

Generally, viscous coupling 10 includes a forward end 12 having meansfor being fixedly coupled to an input shaft (not shown) which is drivenby an output member of the motor vehicle transmission or transfer case.Similarly, an aft end 16 of viscous coupling 10 is provided with anopening 18 for receiving an output shaft (not shown) which is directedto one set of the vehicle's drive wheels (not shown). The output shaftis journally supported for rotation in first and second bearingassemblies 20 and 22, respectively. An elongated hub 24 is shown toconcentrically surround an end portion of the output shaft and isadapted to be fixedly engaged with the output shaft so as to rotatetherewith. More specifically, hub 24 is coupled for rotation with theoutput shaft through splines 26 interiorly formed thereon.

A rotatable drum housing assembly 28 encircles hub 24 and generallyincludes a cylindrical outer drum 30 which is fixedly connected to aforward cover plate 32 and an aft cover plate 34. Forward cover plate 32includes a generally cylindrical axial extension 36 which terminates ina radial flange 38 to which the input shaft is connected. To facilitateattachment of the input shaft, radial flange 38 includes mounting bores40 through which threaded fasteners or the like may be extended. Firstbearing assembly 20, which supports the forwardmost end portion of theoutput shaft, is journaled within an internal portion of the axialextension 36 of forward cover plate 32. Similarly, second bearingassembly 22 is journaled within an internal portion of a generally axialextension 42 of aft cover plate 34. So constructed, drum housingassembly 28 and hub 24 are capable of rotating relative to one another.

Drum housing assembly 28 encloses elongated hub 24 with the innersurfaces of outer drum 30 and forward and aft cover plates 32 and 34,respectively, defining an internal chamber 44. Chamber 44 ishermetically sealed around hub 24 by fore and aft seals 46. Disposedwithin chamber 44 are two sets of interleaved viscous coupling plates,cumulatively designated as 48, which substantially fill chamber 44. Oneset of plates, hereinafter referred to as inner plates 50, are mountedfor rotation with hub 24 while the second set of plates, hereinafterreferred to as outer plates 52, are mounted for rotation with outer drum30.

In general, viscous coupling plates 48 are formed from relatively thinplate stock and are generally ring-shaped. As shown in FIG. 2, eachinner plate 50 includes spline teeth 54 formed along its innercircumference which are configured to meshingly engage axial splines 56formed on the exterior surface of hub 24. Inner plates 50 are positionedin a spaced relationship and are so maintained by spacer rings 58. Withreference also to FIG. 8, outer plates 52 are mounted to outer drum 30via external spline teeth 55 formed around the outer circumference ofouter plates 52. In particular, spline teeth 55 meshingly engage axialsplines 60 formed interiorly of outer drum 30. In the exemplary viscouscoupling apparatus shown, spacer rings 58 are not used with outer plates52 and thus allow axial movement of outer plates 52 between adjacentinner plates 50 along splines 60. However, in one alternativeembodiment, outer plates 52 may be axially spaced by spacer rings 58 andfixed relative to outer drum 30 while inner plates 50 are axiallymovable therebetween along hub 24. Of course, other arrangements ofcoupling plates in a viscous coupling apparatus are known and it shouldbe understood that the present invention is not intended to be limitedto the configuration of the exemplary viscous coupling apparatus shownin FIG. 1.

Chamber 44 is substantially filled, typically 90% or greater, with aviscous fluid such as silicone oil, the remaining volume of chamber 44being filled with air or some other inert gas. To facilitate filling ofchamber 44, aft cover plate 34 is provided with a fill port 62 and fillplug 64.

During operation of viscous coupling apparatus 10, the input shaft willbe driven by the vehicle's source of power or transmission for causingdrum housing assembly 28 and outer plates 52 to rotate. Generally, hub24 and inner plates 50 will be rotating under substantially similarconditions (i.e. the vehicle is traveling on dry pavement with drumhousing assembly 28 rotating with the front wheels while hub 24 isrotating with the rear wheels). Where the conditions involve a slightdifferential in rotational speeds between hub 24 and housing 28, thefluid will permit viscous shearing and accommodate the rotationaldifference by allowing slip. However, as the rotational speeddifferential and viscous shearing rate increase, the apparent viscosityof the fluid will decrease which results in a softening of the fluid.However, this softening is more than offset by the increase in sheartorque generated by the increase in speed and, as the viscous shearingrate increase, viscous coupling 10 becomes increasingly rigid therebytransmitting an increased amount of torque.

If a substantially continuous speed differential is maintained over aperiod of time, the temperature within chamber 44 will begin to increasecausing the viscous fluid to expand. Since the fluid will expand at arate greater than that of chamber 44, the internal pressure of chamber44 will rise. During the rise in chamber pressure, the gas or aircontained within chamber 44 dissolves into the silicone oil. This changein the distribution of air acts to modify its flow patterns and willallow for the development of pressure differentials. In response to thepressure differentials, the axially movable plates (i.e. outer plates 52in the illustrated embodiment) will axially shift and establishfrictional contact with an adjacent non-movable plate (i.e. inner plate50). With the establishment of frictional contact between inner andouter plates 50 and 52, respectively, a sudden and sharp increase intransmitted torque occurs without a corresponding increase indifferential rotational speed. This is referred to as the "humping"phenomenon or torque progression. As is known, the axial movement ofouter plates 52 relative to outer drum 30 is promoted by radiallyextending slots 66 and/or other openings 78 being provided in plates 48to facilitate the development of the pressure differentials.

Prior to discussion of the improvements in viscous coupling plates 48associated with the present invention, a brief summary of conventionallyprocessed plates is warranted. For purposes of clarity, conventionallyprocessed viscous coupling plates, shown in FIGS. 4 through 6, will beidentified as 48'. Typically, viscous coupling plates 48' are stampedfrom plate stock in a machine press utilizing male and female dies. Asseen in FIG. 4, the initial stamping operation produces an uneven fineburr 68 along the edges of one plate surface or face 67 and a rollededge 70 along the edges of the opposing face 69. Uneven burr 68 resultsfrom shearing the plate stock and rolled edge 70 is a result of die rollcaused as the male die moves in the direction as indicated by arrow Xduring the stamping operation.

During the frictional contact of torque progression, fine burr 68 wipesan amount of viscous fluid from the frictionally contacting surfaces ofthe adjacent viscous coupling plate 48' and assists in establishingfrictional contact and torque progression. However, fine burrs 68 aregenerally unevenly formed so as to provide a non-uniform wiping edgeand, in addition, are quickly worn off due to inter-plate frictionalcontact. Without the clearing or wiping action provided by fine burr 68,frictional contact is limited since rolled edges 70 assist inintroducing additional viscous fluid between the facing surfaces ofadjacent viscous coupling plate 48'. Therefore, in conventional viscouscoupling plates, it has been considered desirable to remove rolled edges70 from along the slot of the coupling plate 48'.

One method of removing rolled edges 70 from along slots 66 is to millslots 66 in a secondary machining operation. The cross-section of aviscous coupling plate having a milled edge is illustrated in FIG. 5.While rolled edge 70 is machined off by the milling operation to producea relatively squared corner 72, milling burr 68 is still quickly wornoff during frictional contact with the adjacent plate. Furthermore, themilling procedure has proven difficult and costly to incorporate into arepeatable production setting. Another method of avoiding formation ofthe uneven burr is to bend the entire edge of slot 66 as is shown inFIG. 6. This method produces a substantially even wiping edge surfacehaving an extremely sharp contact point 73. However, the sharp wipingedge may be overly aggressive during wiping action whereby undesirableexcessive wear may occur on the mating plate.

However, removal of rolled edges 70 is not in accordance with theteachings of one embodiment of the present invention. Instead, rollededges 70 are employed as the "wiping" surfaces of the coupling plate.Referring now to FIG. 3, the viscous coupling plates 48 of the presentinvention include complimentary "ramped" or raised surfaces 74 whichterminate adjacent slot 66 at rolled edges 70. In this configuration,rolled edges 70 provide wiping surfaces that avoid the excessivelyaggressive wiping action associated with sharp edges and, therefore, arenot readily susceptible to excessive frictional wear. Alternately,raised surfaces 74 can terminate in a planar or plateau-likeconfiguration such as that described in co-pending U.S. patentapplication Ser. No. 07/891,417, entitled "Viscous Coupling ApparatusWith Coined Plates," which is hereby incorporated by reference.Similarly, raised surfaces 74 do not cause excessive wear on theadjacent frictionally engageable plate. If desired, recessed surfaces80, located adjacent slot 66, may be formed opposite of raised surfaces74. It should be noted that in the configuration of the presentinvention the recessed surfaces 80 do not produce the problem ofintroducing viscous fluid that cannot be wiped away because, unlikeuneven burrs 68, raised surfaces 74 are not readily worn away from thesurface of the viscous coupling plates 48. Also, viscous coupling platesexhibit long wearing characteristics in that it is expected that anysurface wear at rolled edges 70 will cause the arcuate wiping surface toflatten and become planar. As wear continues, the width of the planarwiping surface will increase and provide a progressively larger wipingarea.

To form raised surfaces 74, the areas adjacent to slots 66 of viscouscoupling plates 48 are coined after an initial stamping operation. Assuch, coined surfaces 74 can be readily produced in a progressive diemachine press without removing the initially stamped plates from themachine press itself. For example, the coupling plate is initiallystamped in the direction of arrow Y in a first die set to produce thegeneral configuration of slots 66. The coupling plate is then indexed toa coining die set which causes the edges adjacent to slots 66 to becoined in the direction of arrow Z without removing the initially formedplate 48 from the machine press. Thus, viscous coupling plates 48 can beeasily and economically fabricated in a high volume productionapplication.

As stated above, if the differential rotational speeds continue tooccur, inner and outer plates 50 and 52, respectively, come intofrictional contact as a result of the pressure increase within chamber44. During frictional contact, the rolled edges 70 matingly engage theplanar surface of the adjacent viscous coupling plate for producing awiping action that is operable to effectively remove a significantamount of viscous fluid therefrom. By removing the viscous fluid betweenthe adjacent surfaces of contacting plates 50 and 52, frictional contactis thereby enhanced and increased torque transfer is promoted.

At their radial most ends (inward on inner plates 50 and outward onouter plates 52), slots 66 terminate in circular openings 78. Openings78 are provided, in part, to relieve the stresses involved with thecoining of raised surfaces 74. Coined surfaces 74 are illustrated inFIGS. 2 and 7 as being formed on an inner plate 50 and in FIG. 8 coinedsurfaces 74 are shown formed along slots 66 in outer plates 52.Furthermore, coined surfaces 74 may be formed along any edge whichdefines an opening in coupling plates 48. However, the generally radialorientation shown produces the most significant wiping action in that itis provided normally to the rotational direction of plates 50 and 52.

Turning now to FIGS. 7, 8 and 9, an opposing pair of coupling plates(i.e. inner plate 50 and outer plate 52) are shown. As illustrated inFIG. 9, plates 50 and 52 are positioned such that the coined surfaces 74on each plate face one another. In this configuration, the rotationalspeed differential between inner plate 50 and outer plate 52 generates apumping action which is induced by the raised surfaces 74. The pumpingaction forces the viscous fluid from in between the plates 50 and 52 asshown by arrows P. This, in turn, creates a pressure difference acrossthe moveable outer plate 52 which forces it against the inner plate 50as shown by arrow F. Eventually, the arcuate or planar wiping surface ofeach plate 50 and 52 contacts the surface of the opposing plate andprovides frictional engagement therebetween. As shown in FIG. 7, surfacearea I is the portion of the surface of inner plate 50 that isfrictionally engaged by the coined surfaces 74 of outer plate 52 andsurface area O shown in FIG. 8 is the portion of the surface of outerplate 52 that is contacted by the coined surfaces 74 inner plate 50.

In the configuration of the present invention, the total contact forceis distributed between both the wiping surfaces of the inner plates andthe wiping surfaces of the outer plates, thus increasing the overallcontact surface area than that exhibited in conventional viscouscoupling apparatus. Correspondingly, wear in each individual couplingplate is reduced to thereby increase the useful life of the couplingplates. Also, because both opposing plates assist in the pumping action,the total contact force achievable between adjacent plates issignificantly increased which, in turn, allows the torque capacity foreach pair of coupling plates to likewise be increased.

While the above description constitutes the preferred embodiments of thepresent invention. it will be appreciated that the invention issusceptible to modification, variation and change without departing fromthe proper scope and fair meaning of the accompanying claims.

We claim:
 1. A viscous coupling apparatus comprising a hub adapted forrotation about an axis, a housing enclosing said hub for defining achamber, said housing adapted for rotation relative to said hub aboutsaid axis, two sets of interleaved annular plates in said chamber with afirst set of said plates being rotatable with said hub and a second setof said plates being rotatable with said housing, one of said first andsecond sets being axially movable relative to its corresponding one ofsaid hub and said housing and being capable of frictionally contactingthe other of said first and second sets, a viscous fluid disposed withinsaid chamber and substantially immersing said plates, each of saidplates of said first and second sets comprises a generally planar ringhaving inner and outer peripheries and a plurality of slots formedtherein, portions of said ring located adjacent to opposite edgesurfaces of each of said slots being deformed out of the general planeof said ring for providing a pair of offset portions which defineoppositely inclined planar ramped surfaces relative to the general planeof said ring, each of said ramped surfaces terminating in a wipingsurface formed contiguous to its respective slot edge surface, each ofsaid offset portions having a recessed surface formed opposite at leastone of said ramped surface and said wiping surface, and wherein saidfirst and second sets of plates are disposed within said housing suchthat said offset portions of each set of plates oppose one another andare concentrically positioned.
 2. The viscous coupling apparatus ofclaim 1 wherein said wiping surface is an arcuate wiping surface.
 3. Theviscous coupling apparatus of claim 2 wherein said slots are open at oneof said inner and outer peripheries.
 4. The viscous coupling apparatusof claim 1 wherein said wiping surface is a planar wiping surface. 5.The viscous coupling apparatus of claim 1 wherein said slots are equallyspaced and extend radially at least partly across said ring.
 6. Theviscous coupling apparatus of claim 1 wherein said offset portionincludes a bottom surface substantially parallel to one of said rampedsurfaces.
 7. A viscous coupling apparatus comprising a hub adapted forrotation about an axis, a housing enclosing said hub for defining achamber, said housing adapted for rotation relative to said hub aboutsaid axis, two sets of interleaved annular plates in said chamber with afirst set of said plates being rotatable with said hub and a second setof said plates being rotatable with said housing, one of said first andsecond sets being axially movable relative to its corresponding one ofsaid hub and said housing and being capable of frictionally contactingthe other of said first and second sets, a viscous fluid disposed withinsaid chamber and substantially immersing said plates, each of saidplates of said first and second sets comprises a generally planar ringhaving Inner and outer peripheries and a plurality of slots formedtherein, portions of said ring located adjacent to opposite edgesurfaces of each of said slots being deformed out of the general planeof said ring, each of said deformed portions terminating in a wipingsurface formed contiguous to its respective slot edge surface, andwherein said first and second sets of plates are disposed within saidhousing such that said deformed portions of each set of plates opposeone another and are concentrically positioned.
 8. The viscous couplingapparatus of claim 7 wherein said wiping surface is an arcuate wipingsurface.
 9. The viscous coupling apparatus of claim 7 wherein saidwiping surface is a planar wiping surface.